1. Field of the Invention
The invention relates to an internal combustion engine having an exhaust silencer or muffling system, in particular a silencer with selective variable geometry controlled in accordance with engine data or parameters and to a method of operating such an internal combustion engine having the exhaust silencer with selective variable geometry controlled in accordance with engine data or parameters.
2. Description of Related Art
German patent DE 297 15 756 U1 describes a controllable exhaust silencer in accord with control elements actuated in dependence on the operating state of the internal combustion engine (for example, rotational speed, temperature, load). As a result, the exhaust-gas stream, for different points in operation, can be set to optimum flow speeds and reflection characteristics.
A disadvantage of this solution is that certain operating states of the internal combustion engine are not taken into account. Internal combustion engines which, with the aid of variable valve control, in addition to throttle-free power regulation can also be made to operate in different multi-stroke modes. It is known that an engine can be operated in different multi-stroke modes in order to achieve a reduction in fuel consumption and pollutants. When engine operation changes between the multi-stroke modes, undamped vibrations in the exhaust-gas column or flow through a prior art exhaust silencer or muffler system can result in undesirably loud exhaust noise.
An object of the invention is thus to provide an internal combustion engine with an exhaust silencer or muffling system which achieves optimum sound damping during changing engine operations between multi-stroke modes, and to specify a method of engine operation including the exhaust silencer and muffling system. Reductions in fuel consumption and pollutants by increasing the number of strokes as engine load decreases is noticeable in diesel engines and in gasoline fuelled engines in particular.
This object is achieved by an internal combustion engine having an exhaust silencer or muffling system with selective variable geometry controlled in accordance with engine data or parameters and a method of operating such an internal combustion engine having the exhaust silencer with selective variable geometry controlled in accordance with engine data or parameters.
Since the exhaust silencer has a variable geometry which changes in co-ordination with different multi-stroke modes of engine operation as controlled by actuating elements, the muffling system can accommodate different flow and acoustic characteristics for many different numbers of engine strokes. The system inhibits undamped vibrations of the exhaust-gas column or flow, which would otherwise result in unreasonably high exhaust noise. In addition, it is also possible to have selectively variable co-ordination of the exhaust silencer geometry for different loads and rotational speeds of the engine. By virtue of the effect of the vibrations in the exhaust, it is even possible to improve, inter alia, the full-load engine behaviour.
The subject silencer muffling system co-ordinates the exhaust flow by various means. First, the volume of the silencer can be varied. Second, the cross sections of the flow through the silencer muffling system and/or the lengths of the flow can be varied. This provides a multiplicity of optimisation parameters which, in addition to the acoustic requirements, also allow flexible adaptation of the exhaust silencer muffling system to a desired design and spatial parameters as far as installation in a vehicle is concerned. The exhaust silencer muffling system is calculated in accordance with known acoustic theory, i.e., the Helmholtz resonator.
An electronic control unit, which is present in any case in modern engines, can assume the relatively straightforward additional function of the synchronous control of gas-exchange valves and controlling elements of the exhaust silencer. Serving for this purpose, inter alia, are specific characteristic maps which act activate the control elements in a functionally appropriate manner.
A particularly advantageous method of changing the number of strokes of the engine is by selectively variable valve control, especially by using electromagnetically actuated engine gas-exchange valves. These provide the advantage of quick and stepless adjustment of the valve timing. As a result, in addition to the variation of the number of strokes, it is also possible to realise throttle-free engine regulation and stepless regulation of the compression.
In the silencer muffling system, possible flow control elements are control flaps, control valves and control slides, the selection of which contributes to the flexible solution to the problems of co-ordinating the operation of the exhaust silencer with different engine operations.
Arranging the controllable exhaust silencer downstream of any exhaust-treatment systems, as seen in the flow direction, is advantageous. Examples of an exhaust-treatment device or system is a particle filters (for diesel engines) and/or a catalytic converters.